You're best option here would be to just direct people to the location. You can use the "Add cloud storage" button on the library and point it to where these files should go, and have users just save files there.
A SharePoint library tab is another alternative as well.
You could use flow, for files, but you're asking for a mess to put in rules for changes etc. and I would not recommend trying to "Sync" with flow, especially if there are many changes that could happen.
All files uploaded into Teams are stored already in SharePoint (in the Group Site related to the Team).
I assume you know the above and are asking for those files to be stored elsewhere in a different site in SharePoint? Possible you could use Flow to move files uploaded to one site to be copied over to another site.